A cellular communications network typically includes a variety of communication nodes coupled by wireless or wired connections and accessed through different types of communications channels. Each of the communication nodes includes a protocol stack that processes the data transmitted and received over the communications channels. Depending on the type of communications system, the operation and configuration of the various communication nodes can differ and are often referred to by different names. Such communications systems include, for example, a Code Division Multiple Access 2000 (CDMA2000) system and Universal Mobile Telecommunications System (UMTS).
UMTS is a wireless data communication and telephony standard which describes a set of protocol standards. UMTS sets forth the protocol standards for the transmission of voice and data between a base station (BS) or Node B (cell site) and a mobile or User Equipment (UE). UMTS systems typically include multiple radio network controllers (RNCs). The RNC in UMTS networks provides functions equivalent to the Base Station Controller (BSC) functions in GSM/GPRS networks. However, RNCs may have further capabilities including, for example, autonomously managing handovers without involving mobile switching centers (MSCs) and Serving General Packet Radio Service (GPRS) Support Nodes (SGSNs). The cell site is responsible for air interface processing and some Radio Resource Management functions. The cell site in UMTS networks provides functions equivalent to the Base Transceiver Station (BTS) in GSM/GPRS networks. Cell sites are typically physically co-located with existing GSM base transceiver station (BTS) to reduce the cost of UMTS implementation and minimize planning consent restrictions.
FIG. 1 illustrates a conventional communication system 100 operating in accordance with UMTS protocols. Referring to FIG. 1, the communication system 100 may include a number of cell sites such as cell sites 120, 122 and 124, each serving the communication needs of UEs such as UEs 105 and 110 in their respective coverage area. A cell site may serve a coverage area called a cell, and the cell may be divided into a number of sectors. For ease of explanation, the terminology cell may refer to either the entire coverage area served by a cell site or a single sector of a cell site. Communication from a cell site to a UE is referred to as the forward link or downlink. Communication from a UE to a cell site is referred to as the reverse link or uplink.
The cell sites 120, 122 and 124 are connected to an RNC such as RNCs 130 and 132, and the RNCs are connected to a MSC/SGSN 140. The RNC handles certain call and data handling functions, such as, as discussed above, autonomously managing handovers without involving MSCs and SGSNs. The MSC/SGSN 140 handles routing calls and/or data to other elements (e.g., RNCs 130/132 and cell sites 120/122/124) in the network or to an external network. Further illustrated in FIG. 1 are conventional interfaces Uu, Iub, Iur and Iu between these elements.
A fractional power control (FPC) scheme has been proposed for controlling the mobile or UE transmission power on the uplink of the 3GPP LTE standard. This open loop fraction power control technique proposes setting the UE transmit power spectral density such that a fraction of the path loss (including shadowing) may be compensated. When ignoring a maximum UE transmit power spectral density (power per tone), the UE transmit power spectral density (PSD) P may be established as:P=−αG+Po  (1)where P is the UE PSD, α is an FPC alpha, G is a long term average path gain (in dB) and is common to the uplink and downlink and Po, is a PSD reference quantity that is sent to the UE via downlink signaling.
Using FPC,Po=I+Γ1−(1−α)G0  (2)where I is a long term average received noise plus interference density (in dBm) per physical resource block (PRB) bandwidth, Γ1 is the target SINR (in dB) when α equals one and G0, is a calibration gain in dB.
Using questions (1) and (2), the implied target SINR is:Γ=Γ1+(1−α)(G−G0)  (3)
However, in certain situations, there is no compensation for the path loss and all UEs transmit with the same transmit power spectral density (possible maximum power), which results in high interference levels and poor cell edge rate performance. In other situations, FPC results in traditional slow power control in which the path loss is fully compensated and all UEs are received with the same SINR. This results in poor spectral efficiency, but with good edge rate.
To improve on FPC, relative path gain (RPG) was developed. In RPG, an uplink transmission power is controlled based on a difference of a path loss between the UE and the serving cell site and a path loss between the UE and a next best neighboring cell site. However, RPG takes up a substantial amount of air interface overhead and requires more processing for the UE. Consequently, RPG is not always achievable. More specifically, the UE may only report once or periodically when a ratio of a path loss between the UE and the serving cell site and a path loss between the UE and a next best neighboring cell site exceeds a threshold and may not report at all if the ratio is below the threshold. Thus, there may be a lot of implementation error and air interface overhead when using RPG.
Moreover, the known power control schemes fail to take into account a sum of the actual interfering effects to all of the other neighboring cell sites and require additional overhead.